Ask a chatbot for a source and it will usually hand you one \u2014 a real-looking citation, a specific page number, sometimes even a direct quote. The problem is the source often doesn’t exist. This is an AI hallucination, and most ESL teachers by now have absorbed the basic definition: a language model generating false information with total confidence and no hint of doubt in its tone. What fewer teachers have done is turn that fact into an actual lesson their students experience firsthand. Explaining hallucination in a single paragraph and moving on wastes one of the best critical-thinking opportunities AI has handed language teachers in years. This is a guide to building one class period \u2014 or a short unit \u2014 where students catch an AI in the act of making something up, then use English to prove it.<\/p>\n